Research on the Microstructure and Properties of Coating on Galvannealed High Strength IF Steel

The microstructure, formability and corrosion resistance characters of industrially produced galvannealed coatings on high strength interstitial free (IF) steel with different galvannealing temperature have been investigated. With the galvannealing temperature increases, the Fe content of coating is increase, and the powdering resistance gets weaker while the corrosion resistance gets better. The coating microstructure consisting of a δ phase as the main constituent with a ζ layer on the top surface provides a good powdering resistance. The compact δ and Γ phases are good for the corrosion resistance of coating

The Development of Annealing Time for Super Fine Grain and High Strength IF Steel

The hot rolling, cold rolling and simulative continuous annealing experiments were carried out in the laboratory on the base of new type SFG HSS (super fine grain, high strength steel sheet). The results show that the microstructure which contains a number of cake shaped grain can be refined and homogenized by the feasible annealing holding time. Contrast to the conventional steel, the SFG steel have the characters of super fine grain, high tensile strength, low yield strength/tensile strength rate, good elongation and high r-value high（the plastic strain ratio）．

The Microstructure and Texture of Fine Grain High-Strength IF Steel after Continuous Annealing

In this paper,the fine grain high-strength IF steel after cold-rolling and continuous annealing was studied.The microstructure under different holding time of fine-grain high strength IF steel was observed by the OM and the TEM technology. The influence of texture on continuous annealing time was analysed by Electron Back-Scattering Diffraction (EBSD) technology. It is proposed that the {111} recrystallization texture of fine-grain high strength IF steel is enhanced firstly, and then is weakened along with the increase of holding time, which confirms the strongest {111} texture is occurred at 120s holding time.

Effect of Coiling Temperature and Cold Reduction Ratio on Microstructure and Mechanical Property of Nb Microalloying Added Phosphorus High Strength IF Steel

Nb microalloying added phosphorus high strength IF steel was used to study the effect of coiling temperature and cold reduction ratio on the microstructures and mechanical properties. The experimental results showed that the recrystallization had finished. Under coiling temperature 650°C and cold reduction ratio 75%, and under coiling temperature 600°C or 700°C and cold reduction ratio 65%, the yield strength, tensile strength were lower , the elongation was higher. The plastic strain ratio r value and the strain hardening exponent n value were reached the higher value, respectively, the r value was approximate 1.8, and the n value was approximate 0.26. Therefore, the suggested the optimal coiling temperature is 700°C, cold reduction ratio is 65% to 75%, and it is optimal process of Nb microalloying added phosphorus high strength.